Evaluation of atmospheric profiles derived from single- and zero-difference excess phase processing of BeiDou System radio occultation data of the FY-3C GNOS mission

Abstract

The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the 20 new generation payloads onboard the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. GNOS was designed for acquiring setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou System (BDS) and the U.S. Global Positioning System (GPS). An ultra-stable oscillator with 1-sec stability (Allan deviation) at the level of 10 -12 was 25 installed on FY-3C GNOS, thus both zero-difference and single-difference excess phase processing methods should be feasible for FY-3C GNOS observations. In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing, in satellites. We used a 3-month set of GNOS BDS RO data (October to December 2013) for the evaluation and compared atmospheric bending angle and refractivity profiles, derived from 5 single-and zero-difference excess phase data, against co-located profiles from ECMWF (European Centre for Medium-Range Weather Forecasts) analyses. We also compared against co-located refractivity profiles from radiosondes. The statistical evaluation against these reference data shows that the results from single-and zero-difference processing are consistent in both bias and standard deviation, clearly demonstrating the feasibility of zero-10 differencing for GNOS BDS RO observations. The average bias (and standard deviation) of the bending angle and refractivity profiles were found to be as small as about 0.05%-0.2% (and 0.7%-1.6%) over the upper troposphere and lower stratosphere, including for the GEO, IGSO, and MEO subsets. Zero-differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. The validation results establish that GNOS can 15 provide, on top of GPS RO profiles, accurate and precise BDS RO profiles both from singleand zero-difference processing. The GNOS observations by the series of FY-3 satellites will thus provide important contributions to numerical weather prediction and global climate change analysis.

Quality aspects of the Wegener Center multi-satellite GPS radio occultation record OPSv5.6

“…This work aids the maturation of the RO record with respect to knowledge of data quality and its description (Bates and Privette, 2012) and helps to meet the stringent requirements as defined by the Global Climate Observing System (GCOS, 2010a(GCOS, , b, 2011 for the generation of a climate data record of essential climate variables.…”